Rheostat



May 10, 1938. c, R. scHENK RHEOSTAT Filed Aug. 13, 1955 5 SheetS-Shee. l

v my gw AS Hf M U May 10, 1938. c. R. SCHENK RHEOS TAT 3 sheets-sheet 2 Filed Aug. 13, 1935 Carl Sohenl www:

bly/Y CUM May 10, 1938. c. R. SCHENK 2,117,257

RHEOSTAT Filed Aug. 13, 1955 .3 Sheets-Sheet 3 Patented May 10, 1938 UNITED STATES PATENT OFFICE Singer Manufacturing Company, Elizabeth,

N. J., a corporation of New Jersey y Application August 13, 1935, Serial No. 35,913

Claims.

control mechanism and adapt it for mounting in' a casing of molded phenolic condensation material which thoroughly insulates the rheostat and eliminates all danger of electric shock to the operator.

With the above and other objects in view, as will hereinafter appear, the invention comprises the devices, combinations, and arrangements of l parts hereinafter set forth and illustrated in the accompanying drawings of a preferred embodiment of the invention, from which the several features of the invention and the advantages attained thereby will be readily understood by those skilled in the art.

In the accompanying drawings,l Fig. 1 is a longitudinal vertical section through a rheostat embodying the invention. Fig. 2 is a top plan view of the rheostat. Fig. 3 is a section on the line 33, Fig. 2. Fig. 4 is a section on the line 4 4, Fig. 2. Fig. 5 is a. plan view of the base member of the rheostat casing with the rheostat unit and its operating mechanism mounted thereon. Fig. 6 is a fragmentary bottom plan view of the rheostat. Fig. 7,is a fragmentary bottom plan view of the cover member of the rheostat casing. Fig. 8 is a section on the line 88, Fig. 2. Fig. 9 is a perspective view of one of the feet of the rheostat. Fig. 10 is a perspective view of the fulc'rum support and recovery spring anchorage horns of the rheostat operating lever. Fig. 11 is a. section on the line II-II, Fig. 7. Fig. 12 is a perspective view of the pedal slideblock.

Fig. 13 is a longitudinal vertical section through a modified form of rheostat adapted for mounting on the frame of a sewing machine treadlestand and for connection by a. pull-rod to the treadle of such stand. Fig.A 14 is a front elevation of the rheostat with the cover broken 50 away to show the operating mechanism. Fig. 15

is a section on the line I5-I5, Fig. 13. Fig. 16 is a lower end elevation of the rheostat as shown in Fig. 14. Fig. 17 is a longitudinal section of the operating pull-block of the rheostat shown in 55 Figs. 13 and 14. Fig. 18 is an end elevation of the pull-block, and Fig. 19 is a section on the line I9-I9, Fig. 13.

Referring to the rheostat shown in Figs. 1 to 12, inclusive, which is adapted for operation on the floor, the casing comprises a hollow top or cover member A and a bottom or base member B, each of which is preferably molded in one piece from phenolic condensation material or artificial resin, such as bakelite, which does not soften under heat conditions and has good mechanical strength and high electrical insulating properties. The top member A is preferably of hollow rectangular form and comprises a top Wall I and side walls 2 which latter are formed with internal corner ledges 3. The bottom member B is .substantially flat and preferably of rectangular form and is detachably secured to the top member A, within the side walls 2 of the latter, by means of the corner screws 4 which are screwed into the ledges 3. The bottom member B has rounded corners 5 which are spaced from the rounded internal corner walls 6 of the top member A to form pockets to receive and position the vertical shank 'I of the rubber feet C. The Shanks 'I of the feet C have flanges 8 at their upper ends overlapping the bottom member B and these ilanges are clamped by and between the bottom member B and the ledges 3 of the top member A. The feet C may have at their lower ends the tread portions 9 which may be of annular form and which may underlap the bottom member B.

Mounted on the base member B by means of screws i0 is the usual carbon compression type rheostat unit I I, such as disclosed in the U. S. Patent to Chason, No. 1,643,292; dated Sept. 27, 1927. Such a rheostat unit comprises a porcelain body having spaced parallel wells housing stacks I2 of carbon disks, which stacks are each connected at one end to a terminal screw I3 and at its opposite end to a conducting pressure head I4. The pressure heads I4 are bridged by a Weak bow-spring i5 carried by the operating pull-rod I6 which also carries the stiffer backing spring I'I. The pull-rod I6 is surrounded by the coiled recovery spring I8 which tends to return the pull-rod i6 to the off position shown in Fig. 5 in which the Weak bow-spring I5 is out of engagement with the pressure heads I4 and the circuit through the rheostat is broken. A pull on the rod I6 ist closes the circuit through the rheostat and applies an increasing weak pressure to the stacks I2 of carbon disks which gradually lowers their electrical resistance. Because of the non-rectilinear characteristic curve of a carbon compression resistor it is desirable in the later stages oi movement of the pull-rod I6 to apply greater pressures to the carbon disks than would be possible by the action of the weak bow-spring i6 alone and this is accomplished by the action of the stiffer backing spring I'l. Hence the operative pull upon the rod i6 must increase more rapidly than the distance travelled by the rod i6 in order to overcome the cumulative mechanical resistances offered by the .springs i8, i6 andl1.

The pull-rod i6 has screwed onto its. free end the adjusting nut i6 which is engaged by the strap i9 pivotally connected at 2li to the lever v2i iulcrumed at 22 on the ears 23 of the plate 24 screwed to the base B. The lever 2i has an operating arm '55 which carries a cross-bar 26 to the ends of which are connected the tensioned recov-1 ery springs 2l anchored to the notched horns 2t rising from the plate 2t at opposite sides of the pull-rod i6, nut i8 and pull-strap or stirrupi9. The springs 2l are adjustable along the horns 28 and may each be shifted to any one of the plurality of notches 28' in its respective horn 28.

It will be observed in Fig. 1 that the recovery springs 2l, which are comparatively strong, extend transversely oi the pivotal axis 22 or the lever 2i and that the longitudinal axes of the springs 21 are spaced above the pivotal axis 22 oi said lever. Hence, a down push on the crossbar 26 carries the springs 2l downwardly toward the pivotal axis of the lever 22 and the closer such pivotal axis is approached, the less is the recovery effect` of the springs 21 on such lever. 'I'he weakening effect of the recovery springs 21 on the lever 2i more or less balances the cumulative mechanical resistance of the springs I8, i and i1, so that substantially uniform pressure upon the cross-barv 26 will move the latter through the major portion of its range of motion.

The cover A is formed with a rectangular ver.- tical guideway 29, Fig. rI. in which is fitted the pedal slide 30 slotted or bifurcated at 3| to strad- 'dle the lever 2l and having at its lower end the faces 32 resting on the cross-bar 26. Sto'p lugs 33 on the pedal 30 prevent upward withdrawal of the latter from the guideway. A guide arm 34, Fig. l1, steadies the pedal 30 in the guideway 29.

It will be observed in Figs. 1 and 3 that ventilating space is provided between the edges oi the base B and the side wallsl of the cover A, which latter has Ventilating slots 35 in its top l.

One of the side walls 2 of the cover A is formed with a conductor-cord receiving slot 36, Fig. 7, having a toothed or roughened top wall 31 against which the conductor cord 38 is gripped by the toothed upper face 39o! the tongue 40 on the base B. The cover A is also provided with the foot rest 4l to better enable the operator to con- 'in a substantially vertical position, as showny in Fig. 14, on the frame of a sewing machine treadlestand and operated by a straight pull connection to the treadle member of the stand. In this modiilcation, the -casing comprises a base D and removable hollow cover E housing a carbon compression resistor unit Il identical with that shown in the preceding figures. The pull-rod I6 of this rheostat, adjusting nut I6 and pull-strap I9 are identical with the like parts of the preceding figures, as are the lever 2|, cross-bar 26, fulcruniplate 24 and horns 28, for the recovery springs 21.

The diiierence in the ltwo constructions resides mainly in the substitution for the push-pedal 30 oi' a pull-block 42 molded from phenolic condensation material with the slotted metal insert pullplate 43. The pull-block 42 is connected to the long screw 44 which replaces the short screw 22 of Figs. 1 and 2. The block 42 is slotted in its under side at 46. Pig. 17, to straddle the lever 2 i.. It is also formed with notches 46 to clear the cross-bar 26. The pull-block 42 is guided by the guicleway 41 in the casing. A stop lug 43 on the block 42 arrests the down movement of the latter.

The invention is not to be understood as limited to details of construction and relative arrangements of parts not particularly specified in the appended claims. l

Having thus set forth the nature of the invention, what I claim herein iszi.. The combination with a carbon compression rheostat including a carbon compression resistor. an operating pull-rod, and spring means con trolled by said rod to apply operative pressures to said resistor, a casing' for said resistor, a lever A vmeans to vary the initial spacing of the longitudinal axis of said spring above the pivotal axis of said lever.

2. The combination with a carbon compression rheostat including a carbon compression resistor, an operating pull-rod, and spring means controlled by said rod to apply operative pressures to said resistor, a casing for said resistor, a lever fulcrumed-in said casing and connected to said pull-rod, said `lever having an operating arm, a pedal arranged to depress said arm, and a tension-spring having its longitudinal axis s paced above and extending transversely of the pivotal axis of said lever, said spring being connected at one end to said operating arm, a spring-anchorage arm xed within said casing, the other end of said spring being connected to and shiftable 1ongitudinally of said spring-anchorage arm to vary the spacing betweenthe longitudinal axis of said spring and the pivotal axis of said lever.

3. A rheostatcomprising a hollow casing including a top member of molded phenolic condensation material formed with a guideway, a

bottom member, a manually operated member of molded phenolic condensation material slidably ttingsaid guideway and having a blfurcated end within said casing, a lever fulcrumed on said bottom member within said casing and straddled -by said manually loperated member, a recovery spring connected to said lever, and a carbon compression resistor unit mounted within said casing and having an operating pull-rod connected to said lever.-

4. A rheostat comprising a hollow casing including separable cover and base members, a carbon compression resistance unit mounted within said casing and having an operating pull-rod, an adjusting nut screw-threaded onto said pull-rod, a strap engaging said adjusting nut, a lever fulcrumed on said base and4 connected to said strap,

chorage xed to said base and including spaced horns extending away from said base at opposite sides -of said pull-rod, nut and strap, a pair oi.' tension-springs each connecting an end o! said cross-bar with a respective one of said spaced horns, and manually controlled means to operate said connected lever, strap, nut and pull-rod.

5, The combination with a carbon compression rheostat including a carbon compression resistor, an operating pull-rod, and a spring system controlled by said rod to apply operative pressures to said resistor, a casing for said resistor, a lever iulcrumed in said casing and connected to said pull-rod, said lever having an operating arm, a.

and the pivotal axis oi.' said lever decreasing u throughout the electrical resistance decreasing motion oi' said pedal.

CARL R. SCHENK. 

